Electromagnetic devices



J 25, 1966 D. F. BROWER ETAL ELECTROMAGNETIC DEVICES 2 Sheets-Sheet 1 Filed Nov. 50, 1962 it it Jan. 25, 1966 D. F. BROWER ETAL 3,231,842

ELECTROMAGNETIC DEVICES Filed Nov. 50, 1962 2 Sheets-Sheet 2 m A O L M J M O Z w United States Patent 3,231,842 ELECTROMAGNETIC DEVICES David F. Brewer, San Diego, and Gamma B. Hayward,

Del Mar, Calif., assignors to General Dynamics Corporation, New York, N.Y., a corporation of Delaware Filed Nov. 30, 1962, Ser. No. 241,284 7 Claims. (Cl. 336-182) This invention relates to electromagnetic devices and more particularly to coil construction useful as an air core current transformer or in conjunction with a flux concentrator that efiects the production of high intensity pulsed magnetic fields.

Various advanced experimental and production operations call for the use of extremely high currents or involve the use of high intensity magnetic fields. For we ample, magnetic forming techniques are now being utilized which require high intensity pulsed magnetic fields. Because of the mechanical forces encountered by structures utilized to establish such fields, many of the previously developed structures are relatively complex and structurally cumbersome due to the need for a substantial amount of mechanical reinforcement. Moreover, many of the previously developed structures are relatively inefficient due to high leakage flux and resistive losses encountered during the operation thereof.

It is a prime object of the present invention to provide an improved coil construction useful as a transformer or in conjunction with a flux concentrator.

A further object of the present invention resides in the provision of a coil construction requiring a minimum of mechanical reinforcement and wherein a minimum amount of loss results due to a leakage inductance and wherein resistance losses are minimized.

Still another object resides in the provision of a compact coil construction which is relatively simple to construct and possesses substantial intrinsic mechanical strength.

Other objects and advantages of the present invention will become apparent from the following detailed description when considered in conjunction with the accompanying drawings, wherein:

FIGURE 1 is an end view of a preferred embodiment of the coil construction contemplated by the present invention having a portion thereof broken away to illustrate the internal structure thereof;

FIGURE 2 is an elevated view of the structure illus trated in FIGURE 1, with a portion thereof broken away to better illustrate the removable flux concentrating core that is disposed within the coil construction of the present invention;

FIGURE 3 is an enlarged, cross sectional view taken along the line 3-3 in FIGURE 1;

FIGURE 4 is a schematic of the equivalent electric circuit for the structure disclosed in FIGURES 1 and 2;

FIGURE 5 is a cross-sectional view of another embodiment of the coil construction of the present invention;

FIGURE 6 is an elevational view of the coil construction illustrated in FIGURE 5, with a portion thereof broken away to show the structural relationship between the primary and secondary windings thereof;

FIGURE 7 is a fragmentary view illustrating the structural details of one embodiment of a winding configuration utilized in the coil construction shown in FIG- URES 5 and 6; and,

FIGURE 8 is another embodiment of the Winding configuration disclosed in FIGURE 7.

In general, the present invention relates to the provision of coil construction having a relatively compact configuration and possessing high intrinsic mechanical strength. The coil construction is such that it can be 3,231,842 Patented Jan. 25, 1966 utilized either as an air core transformer or in conjunction with a flux concentrator without the need for bulky structural reinforcement. As contemplated by the present invention, the coil construction comprises a multiturn, spiraled primary winding which is capable of carrying a current of preselected magnitude therethrough so as to induce or set up a current in a secondary winding. The current induced in the secondary winding can be supplied directly to a load or, in the alternative, serve to produce an extremely high intensity pulsed magnetic field.

The secondary winding includes a plurality of elongated conductive members which are interleaved between the turns of the primary winding and are longitudinally separated from each other so that each constitutes a separate secondary turn. All of the turns of the secondary winding are electrically connected in parallel relationship by common secondary conductors, so that the common secondary conductors have current supplied thereto which is approximately equal to the summation of all of the individual currents induced in the interleaved secondary turns. The advantage yielded by this configuration is that an extremely high secondary winding current may be realized, with a minimum of mechanical stress being imparted to the primary coil. At the same time, the coupling between the primary and secondary windings is relatively close and the amount of flux leakage is accordingly small.

Referring in particular to FIGURE 1, the coil construction contemplated by the present invention will be described initially when utilized with a flux concentrator in an electromagnetic device designed to effect the forming of a work piece as a result of the action of a high intensity magnetic field thereon. This latter application can be more fully appreciated if reference is made to the disclosure contained in Patent No. 2,976,907, which issued on March 28, 1961, and/or to the disclosure contained in Patent No. 3,108,325 issued on October 29, 1963, to the common assignee.

Referring to FIGURES 1 and 2, the electromagnetic device includes three basic elements. These are (1) a primary winding 10 which is a suitably insulated multiturn spiraled conductive strip, (2) a secondary winding 11 which includes a plurality of parallelly connected conductive strips that are interleaved between the turns of the primary winding so as to form a unitary coil construction and (3) a conductive fiux concentrator or core 12 which is proportioned with a suitable work space wherein a work piece to be formed is positioned.

More particularly, the primary winding 10 includes a conductor 14 in the form of a strip of a material such as copper which is coated with a layer 16 of suitable insulation such as polyvinyl chloride. The conductor 14 is wound in a flat spiral or coil, with successive ones of the spiraled turns positioned between spaced concentric conductive strips 17 which define a plurality of slots within a split conductive member or housing 18. In this connection, the housing 18, which is either machined from a block of conductive material such as brass, copper, etc. or built up from such conductive material, includes a pair of concentrically arranged inner and outer conductive plates 19 wherebetween the spaced strips 17 are located. The plates 19 and conductive strips 17 extend upwardly from and form an integral part of a base plate 21. A slot 20 is provided across one side of the housing 18 extending through the plates 19, base plate 21 and conductive strips 17.

As previously set forth, the conductor 14 is wound about the concentrically arranged conductive strips 17 in the region between the inner and outer plates 19. The outer extremity of the spiraled conductor extends through a rectangular projecting segment 22 which forms a part of the outer conductive plate 19. The inner end of the spiraled primary winding is suitably soldered or welded in electrical contact with the wall of the plate 19 adjacent the slot 21) so that the projecting section 22 can be utilized as a common potential point for both the inner end of the conductor and the housing 18.

The projecting portion 22 of the outer plate 19 is formed with a rectangular configuration (FIGURE 3) having dimensions somewhat greater than those of the conductor 14. The space between the walls of the rectangular shaped projecting segment 22 and the conductor is filled with a layer 23 of a suitable insulating material such as epoxy which serves as a means for insulating the plate from any mechanical shock that may be experienced by the conductor during production of a high intensity pulsed magnetic field as hereinafter described. Similar insulating material is utilized to cap the inner portion or recessed area of the secondary housing subsequent to the positioning of the primary winding between the conductive strips. In the illustrated embodiment, the conductive flux concentrator or core 12 is preferably formed of a conductive material similar to that of the housing 18. The core is designed to be removably secured in electrical contact with the base plate 21. Accordingly, various sized work pieces can be accommodated by the device merely by interchanging core members. In this connection, the core 12 is proportioned with a main body portion 24 and a lower circular flanged portion 25. The flanged portion 25 is designed to accommodate screws or other fastening members 26, that are utilized to fixedly secure the core 12 in electrical contact with the base plate 21.

As shown, the main body portion 24 of the core 12 is proportioned with an outer diameter that is somewhat smaller than the inner diameter of the housing 18. Accordingly, a small uniform space 28 is provided between the inner surface of the plate 19 and the outer surface 27 ofthe, main body portion of the core. These dimensions of the inner plate 19 and core 12 insure that the core can be read ly Withdrawn and replaced by another memher having a different size and/or shaped work space. However, good electrical contact between the base plate 21 and flanged portion 25 must be insured so that current induced in the secondary housing 18 can be conducted to the core 12 as hereinafter described.

In the embodiment illustrated in FIGURE 2, the central portion of the core 12 is proportioned with a cylindrical work space 31 defined by a wall surface 36. The work space 31 communicates at the opposite extremities thereof with a pair of frusto-conically shaped recesses 32 and 33 that extend outwardly to the oppositely disposed surfaces of the core 12. This configuration is such that the conductive wall surface 36 defining the work space proper is relatively small which is desirable for efficient operation of the device as hereinafter set forth. As shown, the work space 31 is proportioned to accommodate a work piece 34. that is situated therein by suitable mounting means (not shown). To preclude direct electrical contact between the conductive wall surface 36 of the core 12 and the work piece 34, an insulating sleeve 37 is provided on the surface.

Referring to FIGURE 1, the slot 20 provided in the secondary housing extends completely therethrough and is aligned with a similarly proportioned slot 38 that is provided in the core 12. This slot 38 extends from the outer surface 27 of the core 12 to the inner surface 36 and a suitable layer 39 of insulation such as that which serves as the cap for the recessed area of the housing 18 is situated therein. v

The manner in which a high intensity pulsed magnetic field can be produced by the electromagnetic device incorporating the coil construction and flux concentrator will best be understood from a consideration of the schematic diagram depicted in FIGURE 4. In this connection, a high intensity field is established within the work space 31 by passing a high amperage current pulse through the multi-turn primary winding 10. The current pulse is provided by connecting a source of energy 41 such as a capacitor bank or motor generator to the conductor 14 through a pair of conductors 42 and 43. The conductors 42 and 43 are electrically connected to the outwardly extending end of the conductor 14 and to the projecting portion 22 of the outer plate 19. Since the inner end of the conductor 14 is soldered or otherwise electrically connected to the inner plate 19 adjacent the slotted portion thereof, as previously described, a complete path for current flow from the energy source 41 through the primary winding of the coil construction is provided. A suitable switch 44 such as an ignition, thy-ratron, etc. is connected between the primary winding 14 and the energy source 41 which selectively controls the passage of current through the primary winding.

In the illustrated embodiment, the energy source or capacitor bank 41 is initially charged to a high voltage from a high voltage source 46 which is connected across the capacitor bank. A suitable switch 47 is connected in series between the capacitor bank 41 and voltage source 46 to elfect charging of the capacitor bank prior to the time when it is desired to establish the high intensity pulsed magnetic field within the work space 31.

After a work piece 34 is positioned within the work space 31 and assuming that the capacitor bank or energy source 41 has been previously energized, the switch 44 is closed. Consequently, a high amperage current pulse will flow through the primary winding 10 and a high intensity field will be set up around each individual turn of the primary. The fields produced by the high amperage current pulse will intersect each of the conductive strips 17 and the plates 19 and will thereby induce a current flow in each of these members. The induced current generated in the metallic strips 17 and plates 19 will circulate therethrough and pass through the base plate 21 to the core 12.

More particularly, the induced current will circulate through the plates 19 and strips 17 and upon reaching the slot 20 will be conducted downwardly through the base plate 21 to the flanged portion of the core. Thereafter, the current will circulate inwardly along one of the surfaces defining the slot 38 to the inner surface 36 of the core. The circulation path for the induced current is completed by the other slot defining surface of the core 12. Inasmuch as the axial length of the cylindrical surface 36 that defines the work space 31 is relatively small, the density of the cumulative induced current flow across the surface 36 will be extremely high. Consequently, the work space will have a high intensity magnetic field generated therein. In this connection, the magnitude of the pulsed current in the primary Winding is selected so that the intensity of the field established and concentrated within the work space is of sutficient magnitude to suitably form the work piece 34 and effect a reduction in the diameter thereof.

Manifestly, the passage of the high intensity pulsed current through the primary winding and the flow of induced current through the secondary winding and across the inner surface of the core tends to result in the production of numerous diverse mechanical forces which would nor.- mally call for cumbersome reinforcing structures. More particularly, there is a reaction between the fields produced by the primary current flow and fields produced by the passage of induced current through the secondary winding which tends to force the primary and secondary windings apart. In addition, the reaction of the magnetic pressure Within the work space 31 tends to impart a force to the secondary housing 18 through the core 12. The forces resulting from the reaction between the primary and secondary fields are, however, self-compensatmg.

More particularly, the coaction of the primary and secondary fieldswhich-stems fromthe interleaved construction of the windings is such that the current is distributed generally uniformly over the primary and secondary windings which tends to minimize resistive losses during pulsed operation. Moreover, the coil construction produces a generally uniform magnetic field about the windings which minimizes leakage inductance, resistive losses and forces that tend to move the primary winding relative to the secondary winding. In this connection, the net forces imparted to the windings are such that the housing 18 can be easily designed so as to satisfactorily withstand the effects thereof without structural failure.

As previously disclosed, the coil construction contemplated by the present invention can also be satisfactorily utilized as a transformer and the coil construction for this purpose is generally similar to that utilized with the aforedescribed flux concentrator.

Referring in detail to FIGURES 5-7, a preferred embodiment of the coil construction when utilized as a transformer includes a multi-turn primary winding 51 formed of a conductor 51 that is insulated by insulation 52 and is similar to the previously described conductor 14. In addition, the transformer includes a secondary winding 53 formed of a plurality of interleaved conductive strips 54 wherein currents are induced which constitute the cumulative high secondary current, as hereinafter described.

Referring in particular to FIGURES 6 and 7, it can be seen that each conductive secondary strip 54 is a slotted ring of conductive material, i.e., copper, brass, etc. having enlarged upper and lower segments 55 and 56. The segments 55 and 56 are joined by a thin walled central section 57 whereto a portion of the conductor 51 is suitably secured as by cementing or the like. The segments 55 and 56 extend from the thin walled central section a sufficient distance so that the surfaces thereof are substantially aligned with the outer surface of the segment of the conductor situated therein.

Preferably, the conductive strips 54 are fabricated from an extruded strip which is cut to desired length and subsequently bent into the ring like configuration. One preferred mode of fabricating the interleaved structure is to initially cut the individual strips 54 with varying lengths to accommodate the reduced radius of each turn so that the ends of the strips, when formed in the spiral configuration, are aligned to provide a slot 58 therebetween.

Thereafter, a length of the conductor 51 is chosen so that it properly coincides with the desired dimensions of the primary transformer winding. The individual extruded strips are joined to one longitudinal face of the conductor with a uniform space between each of the successive strips. After the conductor is set in positive contact with the thin walled section 57 of each of the strips 54, the entire elongated unit is formed as by spiraling or coiling about a suitable mandrel. Finally, the coiled or spiraled interleaved primary and secondary turns are joined and secured together by a suitable fastening means, i.e., rivets 59.

Preferably, the outermost conductive strip 54 is provided with a pair of terminals 60 and 61 near the opposite extremities thereof adjacent the slot 58. More particularly, the terminals 60 and 61 extend from and are electrically connected to the enlarged upper segment 55 of the conductive strip 54. The terminals serve as a means for connecting the secondary to a suitable load (not shown).

When a suitable source of electrical energy is connected to the inner and outer extremities of the conductor 51 thereby initiating the flow of primary current therethrough, individual current components will be induced in each of the conductive secondary strips 54. These individual current components will circulate through the strips 54 and will be supplied to the aforementioned load which will be attached to the terminals 60 and 61.

An alternate construction of the strips 54- which constitute the parallely connected secondary turns is illustrated in FIGURE 8. This construction consists cssentially of a strip of extruded material such as brass, beryllium, copper, etc. which has the edges thereof folded so as to define a central region wherein the conductor 51 is positioned.

The equivalent circuit for a transformer of the type previously described is essentially the same as that illustrated in FIGURE 4. However, the secondary winding of the coil construction, when used as an air core transformer, would be electrically connected to a suitable load whereto a cumulative current would be supplied as a consequence of the summation of the individual currents induced in each secondary turn. In this connection, the transformer could be utilized to supply high current pulses to the load or an alternating current of high intensity. The latter choice will be dictated by the particular use to which the transformer would be put. It should be noted that, irrespective to the use of the transformer, it would be extremely sturdy in construction and relatively economical to fabricate. In addition, the self-compensating feature whereby harmful mechanical forces are minimized yield the same advantages in the transformer construction as those realized when utilizing the coil construction in conjunction with the flux concentrator.

It should be understood that various modifications in the structural configuration of the embodiments previously described can be effected by one skilled in the art without deviating from the invention as set forth in the following claims.

What is claimed is:

1. An electromagnetic device which comprises an insulated multi-turn primary winding including a spiral wrapped strip of conductive material with spaced regions being defined between successive spiraled turns, a secondary winding including a plurality of elongated conductive strips, said conductive strips being interleaved between successive spiraled turns of said primary winding and longitudinally spaced from each other with the respective ends thereof being approximately in radial alignment, and means electrically connecting the respective aligned ends together so that said strips are electrically connected in parallel relation whereby a cumulative high current is produced in said secondary winding as a result of the summation of the individual components of current induced in said conductive strips.

2, An electromagnetic device capable of effecting magnetic forming operations through the buildup of an intense magnetic field that is applied to a work piece so as to accomplish the desired shaping thereof, which device comprises a conductive core member having a hollow work space defined by an inner surface along the axis thereof, a multi-turn primary winding disposed in coaxial relation about the outer surface of said core, including an insulated spiral wrapped strip of conductive material with spaced regions being defined between the successive spiraled turns thereof, and a secondary winding including a plurality of elongated conductive strips, said conductive strips being interleaved between the turns of said primary winding in the regions defined therebetween and longitudinally spaced from each other each constituting a separate secondary turn, with the respective ends thereof being approximately in radial alignment means for electrically connecting the respective aligned ends together so that said conductive strip-s are electrically connected in parallel relation, and means for maintaining said strips in direct electrical contact with said core so that the passage of current through said primary winding induces a current in said secondary strips that is passed to said core and conducted across the surface defining the work space to produce an intense magnetic field.

3. An electromagnetic device capable of effecting magnetic forming operations through the buildup of an intense magnetic field that is applied to a work piece so as to accomplish the desired shaping thereof, which device comprises a conductive core member having a hollow work space defined by an inner surface along the axis thereof, a multi-turn primary Winding including an insulated spiral wrapped strip of conductive material with spaced regions being defined between the successive spiraled turns thereof, a split conductive housing disposed concentrically about said core merrrber, means electrically connecting the housing to said conductive core memher, said split conductive housing including a plurality of spaced concentric conductive strips with the respective ends thereof being approximately in radial alignment, said strips defining a plurality of slots within the housing so that said primary winding can be disposed therein with the conductive strips interleaved between the turns of said primary winding, and means for electrically connecting the respective aligned ends together so that said conductive strips are electrically connected in parallel relation whereby the passage of current through said primary winding induces a current in said conductive strips that is conducted through said housing to said core member and across the surface defining the work space to produce an intense magnetic field.

4. An electromagnetic device which comprises a multiturn primary winding including an insulated spiral wrapped strip of conductivematerial with spaced regions being defined between successive spiraled turns, and a secondary winding including a plurality of elongated conductive strips of uniformly varying length, said conducrtive strips having central sections of reduced cross section wherein successive spiraled turns of said primary winding are disposed and maintained, said conductive strips having respective ends approximately in radial alignment and means for electrically connecting the respective aligned ends together so that said strips are electrically connected in parallel whereby the flow of current through said primary winding induces current flow in each of said conductive strips.

5. An electromagnetic device capable of effecting magnetic forming operations through the buildup of an intense magnetic field that is applied to a workpiece so as to accomplish the desired shaping thereof, which device comprises a conductive core member having a hollow workspace defined by an inner surface along the axis thereof, a conductive annular housing disposed concentrically about said conductive core member, said housing having a radially extending slot therein and having a generally U-shaped cross sectional configuration, means electrically connecting said housing to said conductive core member, a multi-turn primary winding disposed within said housing and including an insulated spiral wrapped strip of conductive material with spaced regions being defined between successive spiraled turns thereof, a plurality of elongated conductive strips disposed in said housing and interleaved in said spaced regions in longitudinally spaced relationship, the longitudinal edges of the strips being in electrical contact with the housing and the respective ends of said strips being approximately in radial alignment to define a slot which is in radial alignment with the slot in the housing, whereby the passage of current through said primary winding induces a current in said conductive strips that is conducted through said housing to said core member and across the surface defining the workspace to produce an intense magnetic field.

6. An electromagnetic device which comprises a sec ondary winding including a plurality of longitudinally spaced elongated conductive strips disposed in a spiral configuration with the respective ends thereof in generally radially aligned-relationship, each of said strips having raised electrically conductive sections at the marginal edges thereof which spaces the intermediate section thereof from the intermediate sections of adjacent strips and electrically couples the strips together, and a multiturn primary winding including an insulated'strip of conductive material disposed in the spaces defined between the secondary conductive strips.

7. An electromagnetic device which comprisesa secondary winding including a plurality of longitudinally spaced, elongated conductive strips disposed in a spiral configuration with the respective ends thereof in generally radially aligned relationship, each of said strips having inwardly folded electrically conductive sections at the marginal edges thereof which spaces the intermediate section thereof from the intermediate section of adjacent strips and electrically couples the strips together, and a multi-turn primary winding including an insulated strip of conductive material disposed in the spaces defined between the secondary conductive strips.

References Cited by the Examiner UNITED STATES PATENTS 2,599,182 6/1952 Kerns 336-182 2,655,623 10/1953 Parker 336182 BERNARD A. GILHEANY, Primary Examiner.

JOHN F. BURNS, LARAMIE E. ASKIN, Examiners. 

1. AN ELECTROMAGNETIC DEVICE WHICH COMPRISES AN INSULATED MULTI-TURN PRIMARY WINDING INCLUDING A SPIRAL WRAPPED STRIP OF CONDUCTIVE MATERIAL WITH SPACED REGIONS BEING DEFINED BETWEEN SUCCESSIVE SPIRAL TURNS, A SECONDARY WINDING INCLUDING A PLURALITY OF ELONGATED CONDUCTIVE STRIPS, SAID CONDUCTIVE STRIPS BEING INTERLEAVED BETWEEN SUCCESSIVE SPIRALED TURNS OF SAID PRIMARY WINDING AND LONGITUDINALLY SPACED FROM EACH OTHER WITH THE RESPECTIVE ENDS THEREOF BEING APPROXIMATELY IN RADIAL ALIGNMENT, AND MEANS ELECTRICALLY CONNECTING THE RESPECTIVE ALIGNED ENDS TOGETHER SO THAT SAID STRIPS ARE ELECTRICALLY CONNECTED IN PARALLEL RELATION WHEREBY A CUMULATIVE HIGH CURRENT IS PRODUCED IN SAID SECONDARY WINDING AS A RESULT OF THE SUMMATION OF THE INDIVIDUAL COMPONENTS OF CURRENT INDUCED IN SAID CONDUCTIVE STRIPS. 